In light of the recent rise in terrorism, governments around the world have become increasingly concerned about the effects of chemical warfare agents, biological agents, industrial chemicals and other highly toxic materials. Because nations stockpile such materials for both industrial uses and as warfare agents, such biological and chemical contaminants represent a potential hazard to armed forces and civilian populations alike, through direct exposure and through environmental contamination.
Commonly known chemical warfare agents include organosulfur-based compounds such as 2,2′-Dichlorodiethyl sulfide (HD, mustard, mustard gas, S mustard or sulfur mustard), which are known as “blister” or “blistering” agents and can be lethal in high doses. Other chemical warfare agents include organophosphorus-based (“OP”) compounds, such as O-ethyl S-(2-diisopropylamino)ethyl methylphosphonothiolate (VX), 2-Propyl methylphosphonofluoridate (GB or Sarin), and 3,3′-Dimethyl-2-butyl methylphosphonolluoridate (GD or Soman), which are commonly referred to as “nerve” agents because they attack the central nervous system and can cause paralysis and potentially death in a short period of time. Other chemical contaminants include certain industrial chemicals, insecticides and pesticides such as parathion, paraoxon and malathion, which can also have harmful effects.
Methods and materials for decontaminating surfaces exposed to such warfare agents are known in the art. Yang et al., “Decontamination of Chemical Warfare Agents”, Chem. Rev. Vol. 92, pp 1729-1743 (1992). These decontaminant solutions and materials tend to function by chemically reacting with and/or adsorbing the agents. Early chemical-based decontaminants included bleaching powders, potassium permanganate, superchlorinated bleaches, and solutions containing alkali salts such as sodium carbonate, sodium hydroxide and potassium hydroxide. Many of these decontaminant compositions tend to have certain undesirable properties, including corrosiveness, flammability and toxicity. Additionally, some chemical-based decontaminants degrade upon exposure to water and carbon dioxide, requiring that the solution be prepared and used contemporaneously with its use.
Much of the research to date concerning biological and chemical agents has focused on the immediate need to decontaminate the surfaces that have been exposed to the agent. As a result, while the methods and compositions are designed for decontaminating vehicles, equipment, personnel and the like, they are not well suited or effective at removing, deactivating or detoxifying biological and chemical contaminants in air or other breathing gases.
Basic methods used to control air quality have included physical filtration, absorption on solid sorbents such as activated carbon, electrostatic precipitation, chemical conversion such as through the use of ozone, and treatment with various forms of radiation including heat, ultraviolet light and microwave. Filtration methods tend to be limited by the pore size of the filters, and are generally not capable of removing many biological and chemical contaminants. Moreover, ultra small pore sizes and clogging due to particulates on the filter can cause an unacceptable pressure drop across the filter for many applications. Electrostatic precipitation of particles works by charging the particles and then removing them from a gas stream onto an oppositely charged surface such as on a collection plate. This technique is not suitable for high velocity gas streams, for fluids containing volatile chemical contaminants or contaminants that are otherwise difficult to charge. Chemical reaction such as through the use of ozone is typically effective on only small volumes of gas and is impractical for many applications. Heating, although effective for removing many types of biological and chemical contaminants from gas, tends to be ineffective on higher velocity gas streams. Ultraviolet light is also effective but can be difficult to implement on larger gas volumes as the light tends to only be effective on those contaminants in the portion of the gas stream immediately adjacent the light source.
Adsorption of gases by sorbents can be effective where the sorbent is specifically matched to the gases. For example, activated carbon requires that carbon particle characteristics be matched to the properties of the gases to be adsorbed. However, what is needed is a solid sorbent that is capable of sorbing a diverse set of biological and chemical contaminants such as bacteria, viruses, nerve agents, blister agents, pesticides, insecticides and other highly toxic chemical agents from various gases, which can easily be incorporated into a variety of gas treating apparatuses.